Many model systems study eariy development of animals with the goal to understand the normal mechanisms of morphogenesis. This is important because early in development the cells ofthe embryo exhibit a series of dramafic cell rearrangements that establish the primitive body plan ofthe animal. This complex sequence is quite robust yet is thought to t)e the source of many unexplained human birth defects. A number of approaches have attempted to understand and reduce those defects, but perhaps the best research direction in the long run is to thoroughly understand how embryos normally transect these eariy developmental stages. In this project the goal is to understand in a model system, the sea urchin, how the eariiest gene regulatory network controls cellular processes that contribute to morphogenesis, patterning and reprogramming. The control machinery of development are the transcriptional networks that regulate all cellular acfivifies. Among the best-understood gene regulatory networks (GRNs) is the one that governs specificafion of early sea urchin development up to the beginning of gastrulation. This project will take advantage of that knowledge to examine how the next steps of development are controlled. The idea is that sub-circuits ofthe endomesoderm GRN control morphoregulator molecule expression, and these in turn control the cell biological processes that conduct morphogenetic movements, pattern the skeleton, and control a capacity for cellular reprogramming in the embryo. Three specific aims will be pursued. The first will be to use the GRN, transcriptomes, gene candidate lists, and perturbafions to identify the morphoregulators that control the several phases of archenteron invaginafion. The second aim will be to examine how the GRN controls release of signals from the ectoderm in such a precise manner that enables the skeletogenic cells to produce a correcfiy patterned skeleton. The third aim will examine how the state of the GRN is able to shift as it reprograms. There the goal will be to identify a repressor of reprogramming, and also to record the state changes as the GRN shifts from one specificafion state to another. Each of these aims draws upon the advanced state of understanding of the sea urchin gene regulatory network.